Does Reverse Osmosis Remove Alkalinity? Let’s Find Out!

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Reverse osmosis is a very thorough form of water purification that removes most things from H2O, leaving you with an incredibly pure final product.

So, it makes sense that while it removes all the bad stuff, maybe it is removing things from the water that you might actually wish stayed in there, which are the chemicals that contribute to a water’s alkalinity.

But does reverse osmosis really remove alkalinity from water? Let’s see.

Key Takeaways

  • Yes, reverse osmosis removes the chemicals contributing to a water’s alkalinity.

Does Reverse Osmosis Remove Alkalinity from Water?

So, does reverse osmosis remove alkalinity from water?

Alkalinity is based on certain chemicals in water like hydroxides, carbonates, and bicarbonates.

So yes, reverse osmosis being a powerful water purification process effectively removes most of these chemicals effectively removing alkalinity from water.

The alkalinity chemicals are left behind and discarded with the wastewater and other impurities/contaminants.

Under Sink Reverse Osmosis System

What Is Water Alkalinity?

Water alkalinity is “the buffering capacity of a water body; a measure of the ability of the water body to neutralize acids and bases and thus maintain a fairly stable pH level”. (Source)

As mentioned before, this property is depending on certain chemicals in the water (hydroxides and (bi-)carbonates among others).

Alkalinity may be necessary for certain things, such as maintaining aquatic life, as it provides a buffering system that sustains the pH levels within a range suitable for the survival of the organisms in an aquarium.

Alkalinity vs pH

pH and alkalinity are two chemistry concepts that can be misunderstood. The pH scale measures acidity or basicity, while alkalinity reflects a solution’s capacity to neutralize acids and bases.

In other words, pH is a measurement of the concentration of hydrogen/hydroxide ions in a solution; the more the hydrogen ions, the more acidic it is and the more the hydroxide ions, the more alkaline (or basic) it is. Neutral substances have a pH of 7, with values lower showing acidity and higher, indicating basicity. The pH scale measures from 0 to 14, and each point’s difference represents ten times more basicity or acidity.

Alkalinity, however, refers to a solution’s capacity to prevent pH changes caused by added acids or bases.

Is Reverse Osmosis Water Alkaline or Acidic, and Why?

Reverse osmosis water usually has a pH level below 7, thus qualifying it as an acid. Depending on a few factors, the exact pH value may fluctuate; however, it typically falls between 5.5 and 6.5. To put this into perspective, coffee is around 3, meaning that while reverse osmosis water may be considered acidic, it is relatively less so than most other beverages.

Reverse osmosis water is acidic due to two primary reasons:

  1. Removing alkaline minerals such as calcium and magnesium contributes to this acidity.
  2. Secondly, when the water is exposed to air, it readily absorbs carbon dioxide, producing weak carbonic acid.

How You Can Test Your RO Water’s Alkalinity

Measuring the alkalinity of water is done by a process known as titration, where the quantity of acid needed to lower the pH of a water sample to 4.5 is determined. This is accomplished by gradually adding small amounts of acid until the water attains the desired pH level.

Measuring feed water alkalinity is crucial to predict the likelihood of carbonate scaling on your reverse osmosis membrane. Any pH level beyond 8.3 renders your water more susceptible to scaling.

How to Make Reverse Osmosis Water More Alkaline?

If the thought of RO water being a weak acid freaks you out, fear not. There are simple ways to make your water more alkaline and increase its mineral content. Adding minerals such as magnesium and calcium back into the water in the final stage of the RO system is the key and will bring the pH back up to a 7-7.5 or higher.

So the most efficient way to remineralize your reverse osmosis water is by adding a remineralization filter to your RO filtration system. This extra step is just after the RO membrane and contains media that adds the minerals back into the water before it passes through to your reverse osmosis faucet.

An alternative is to supplement the filtered water with an electrolyte blend or mineral drops. Although cost-effective, it adds extra steps to your process as you must remember to manually add the drops or blends before drinking the water.

woman sitting in front of water glass

Other Water Treatment Methods That Remove Alkalinity


Distillation effectively removes alkalinity by evaporating water and condensing it back to its liquid form while leaving behind the alkaline chemicals.

Deionization (Demineralization)

Water deionization is the process of removing ions and other impurities from water. The most common deionization method is using an ion-exchange resin that attracts and removes electrically charged ions present in the water.

This process exchanges any salt/mineral ions in the water with hydrogen or hydroxyl ions, producing pure water. This type of water is vital to many applications, including medical equipment sterilization and drug manufacturing.

If you have any thoughts about the question, does reverse osmosis remove alkalinity, please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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